In the past, GPS receivers have frequently used analog carrier injection demodulation schemes to demodulate the down converted digital GPS signal. The miniature GPS receiver (MGR) described in an article entitled "A Miniature GPS Receiver" by N. B. Hemesath et al in Volume 30, Number 9, Microwave Journal September 1987, starting at page 81, is one of the first GPS receivers that utilizes digital demodulation techniques, it uses a 3-level carrier injection demodulation scheme. A more detailed description of the GPS chip set contained therein was discussed in a paper entitled "DARPA'S Advanced Technology Chip Set" presented by N. B. Hemesath and J. M. H. Bruckner at the ION Satellite Division International Technical Meeting in Colorado Springs, Colo., September 1988; the above referenced article and paper are hereby incorporated herein by these references.
Also in the past, it has been proposed to improve performance of GPS receivers (ie reduce the signal loss) by increasing to a 5 or 7-level carrier injection signal demodulation scheme. However, such schemes with their 5-level or 7-level mixers require much more complicated gate systems and consequently are more expensive and consume more power.
Consequently, there exists a need for improved GPS receivers, which have enhanced performance without excessively complicated gate systems and their associated need for power.